2. Temperature, Pressure, and Density Danielle Hettmann and Chris Saleh SYST460 – Fall 2011

3. Static temperature: measure of the temperature at the surface of the aircraft Ambient temperature: measure of the temperature of the air in the region surrounding the aircraft

4. rule of thumb: ambient temperature drops 1 ˚ C for every 1000 feet increase in altitude Ambient temperature varies with altitude: Below 36,089 feet: ambient temperature (˚R) = -3.566˚ * (altitude/1000) Above 36,089 feet: ambient temperature (˚R) = 389.988˚ Temperature Ratio Below 36,089 feet, Tamb/TSeaLevel = θ = 1 – (6.8753 X 10 ^-6) * pressure altitude Above 36, 089 feet, Tamb/TSeaLevel = θ = 0.7519 Delta ISA θ = (T amb + ∆ISA) / (T SeaLevel + ∆ISA)

5. Static Pressure: Measure of the pressure at the surface of the aircraft Ambient Pressure: Measure of the pressure of the air in the region surrounding the aircraft

6. Pressure Ratio :  =P amb / P SeaLevel Below 36,089 feet, the Ambient Pressure (lb/ft2) = (1 - ˚ * 6.88 X 10 -6 * Pressure Altitude) 5.26 Above 36,089 feet, the Ambient Pressure (lb/ft2) = 0.223360 e ( (36.089 – Pressure Altitude)/20.8057)

7. Ambient Density: Measure of the density of the air in the region surrounding the aircraft Density Ratio: =  (Slugs/ft3) =  amb /  SeaLevel Boyles Law: Density (  ), pressure (  ), temperature (θ)  =  / θ